There's a loophole in how most hybrid gasoline-electric vehicles work, and countless gallons of gasoline are draining out of them.

Running the front defroster increases their fuel consumption drastically, as I discovered while driving three of them during Detroit's typically cold winter. Setting the air-conditioning on maximum cool has the same effect, so the problem is not limited to Northern regions.

The hybrids fell as much as 40 percent below the EPA mileage figures for combined city and highway driving during my recent test, which covered a mix of Detroit-area roads.

All three vehicles I drove probably got somewhat better fuel economy in my test than if I'd been driving conventional models, but this is just the latest example of hybrids falling short of the hype that surrounds them.